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Abstract:

A method for determining alignment of light and an X-ray fields of an
X-ray apparatus, comprising: directing the light field onto an exposure
area, positioning a scale and an X-ray indicating element in association
with each other at the exposure area such that said scale and X-ray
indicating element cross an edge of the light field, wherein said X-ray
indicating element emits light upon exposure to X-rays so that parts
exposed to X-rays can be distinguished from non-exposed parts,
determining a position on the scale where the light field edge is
positioned, and directing the X-ray field onto the exposure area. The
method comprises generating an image of the scale and the X-ray
indicating element using a digital camera, determining a position on the
scale where an edge of the X-ray field is positioned, and comparing the
scale positions of the edges of the light and X-ray fields.

Claims:

1. Method for determining alignment of a light field and an X-ray field
of an X-ray apparatus, comprising the steps of: directing the light field
onto an exposure area, positioning a scale and an X-ray indicating
element in association with each other at the exposure area such that
said scale and X-ray indicating element cross an edge of the light field,
wherein said X-ray indicating element is configured to emit light upon
exposure to X-rays in such a way that parts exposed to X-rays can be
distinguished from non-exposed parts, determining a position on the scale
where the light field edge is positioned, directing the X-ray field onto
the exposure area, generating an image of the scale and the X-ray
indicating element when the X-ray indicating element emits light due to
the exposure of said X-ray field using a digital camera, determining a
position on the scale where an edge of the X-ray field is positioned by
analyzing said image, and comparing the scale positions of the edges of
the light and X-ray fields.

2. Method according to claim 1, wherein the step of generating an image
of the scale and the X-ray indicating element comprises steps of:
recording the X-ray exposure with a digital video camera, and selecting
an image from the video recording.

3. Method according to claim 1, comprising a step of registering the
position of the light field edge by placing a marker that indicates said
position on the scale.

4. Method according to claim 1, comprising a step of registering the
position of the light field edge by generating an image of the scale and
the edge of the light field using said camera.

5. Method according to claim 1, wherein the step of determining a
position on the scale where an edge of the X-ray field is positioned by
analyzing said image comprises a step of viewing the image on a computer
screen using image/video processing software.

6. An apparatus for determining alignment of a light field and an X-ray
field of an X-ray apparatus, said arrangement comprising an X-ray
indicating element configured to emit light upon exposure to X-rays in
such a way that parts exposed to X-rays can be distinguished from
non-exposed parts, and a scale arranged in association with the X-ray
indicating element, wherein said element and scale are configured to
allow placement on an exposure area for said light and X-ray fields such
as to allow determination of where on the scale an edge of the light
field and an edge of the X-ray field are positioned when said fields are
directed onto said exposure area, wherein the apparatus comprises a
digital camera arranged to generate an image of the scale and the X-ray
indicating element when the X-ray indicating element emits light due to
an exposure of said X-ray field.

7. An apparatus according to claim 6, wherein the camera is a digital
video camera.

8. An apparatus according to claim 6, wherein the camera is fixed to a
flexible arm that allows the position of the camera to be adjusted.

9. An apparatus according to claim 6, comprising at least one marker for
indicating on the scale the position of the edge of the light field,
wherein said at least one marker is X-ray detectable.

10. An apparatus according to claim 6, comprising means for allowing
visualization of the image or images recorded by the camera.

11. Device for determining alignment of a light field and an X-ray field
of an X-ray apparatus, said device comprising an X-ray indicating element
configured to emit light upon exposure to X-rays in such a way that parts
exposed to X-rays can be distinguished from non-exposed parts, and a
visible scale arranged in association with the X-ray indicating element
such as to allow determination of where on the scale an edge of the light
field and an edge of the X-ray field are positioned, wherein the device
comprises a first and a second unit, wherein each of said units comprises
a set of said X-ray indicating element and scale, and wherein said first
and second units are rotatably connected to each other.

12. Device according to claim 11, comprising four units, each of which
have an elongated shape and comprise a set of said X-ray indicating
element and scale, wherein said four units are rotatably connected to
each other such as to allow formation of a cross and to allow positioning
on top of each other.

13. Device according to claim 11, wherein the X-ray indicating element is
capable of fluorescing upon exposure to X-rays.

Description:

TECHNICAL FIELD

[0001] This invention relates to a method and equipment for determining
alignment of a light field and an X-ray field of an X-ray apparatus.

BACKGROUND OF THE INVENTION

[0002] Checking of the actual distribution of an X-ray field in comparison
to a set value is an important and legally regulated test for X-ray
equipment used in e.g. radiography, mammography and therapy. Significant
discrepancies between actual and presumed X-ray field distributions may
result in additional exposure to X-rays and unnecessary doses.

[0003] It is common that an X-ray equipment is provided with a light
source that is arranged to produce a light field that has a similar
distribution as the X-ray field. This light field can be used instead of
the X-ray field when adjusting e.g. the area to be exposed or the
position of a patient.

[0004] To make use of such a light field it is important that the light
and X-ray fields are well aligned with each other. For this reason it is
important that the equipment is calibrated, which calibration involves
the use of suitable means and methods for determining to what extent the
two fields coincide. In such a determination it is needed to somehow
visualize the X-ray field such as to allow comparison of the two fields.

[0005] Conventionally, X-ray films have been used to determine the
distribution of the X-ray field. To avoid the time and effort associated
with the development of such films some alternative devices have been
presented.

[0006] In one example, the device is provided with an afterglowing
phosphor screen that visualises the X-ray radiation field. To determine
the deviation between the two fields the device is initially adjusted to
the light field according to certain marks. After exposing the device to
X-ray the afterglow shows the size and position of the X-ray field. A
scale on the device shows the magnitude of any deviation from the light
field.

[0007] US 2006/0285646 shows another example wherein a device in the form
of an X-ray "ruler" is provided with a scale in the form of a row of
X-ray sensors connected to a corresponding light-emitting element. This
device is intended to be placed at an edge and half-way into the light
field. When exposed to the X-ray field the light-emitting elements show
where the edge of the X-ray device was positioned during exposure.

[0008] Although the type of devices exemplified above has simplified the
procedure compared to the use of X-ray films, there is still a need for
improvements in this technical area.

SUMMARY OF THE INVENTION

[0009] An object of this invention is to provide a method and equipment
that allows for a more efficient procedure for determining alignment of
light and X-ray fields of an X-ray apparatus. This object is achieved by
the method, arrangement and device defined by the technical features
contained in independent claims 1, 6 and 11. The dependent claims contain
advantageous embodiments, further developments and variants of the
invention.

[0010] The invention concerns a method for determining alignment of a
light field and an X-ray field of an X-ray apparatus, comprising the
steps of: directing the light field onto an exposure area; positioning a
scale and an X-ray indicating element in association with each other at
the exposure area such that said scale and X-ray indicating element cross
an edge of the light field, wherein said X-ray indicating element is
configured to emit light upon exposure to X-rays in such a way that parts
exposed to X-rays can be distinguished from non-exposed parts;
determining a position on the scale where the light field edge is
positioned; and directing the X-ray field onto the exposure area.

[0011] The inventive method comprises the steps of: generating an image of
the scale and the X-ray indicating element when the X-ray indicating
element emits light due to the exposure of said X-ray field using a
digital camera; determining a position on the scale where an edge of the
X-ray field is positioned by analyzing said image; and comparing the
scale positions of the edges of the light and X-ray fields.

[0012] An advantageous effect of this method is that it allows for a
simple procedure since digital images are easy to handle and easy to
analyze on a computer screen. Further, the method is flexible since
analysis can be carried out at a later stage and in another location as
digital images are easy to store and transfer. In addition, the inventive
method provides for a very rapid and easy documentation of the results in
that the image is quickly and easily stored.

[0013] In a preferred embodiment of the invention the step of generating
the image comprises the steps of: recording the X-ray exposure with a
digital video camera; and selecting an image from the video recording. A
video camera can be started before and stopped after the X-ray exposure
and digital video recordings allows for analysis image by image. Thereby
it is possible to select a proper image without any need for
synchronizing the trigging of the camera with the X-ray exposure.

[0014] Analyzing the image by viewing the image on a computer screen using
image/video processing software has the advantage that no complicated
algorithms that take account of different camera positions are needed, as
is the case when using computerized procedures for analyzing the image.
The camera can thereby be relatively freely adjusted.

[0015] The invention also concerns an arrangement for determining
alignment of a light field and an X-ray field of an X-ray apparatus, said
arrangement comprising an X-ray indicating element configured to emit
light upon exposure to X-rays in such a way that parts exposed to X-rays
can be distinguished from non-exposed parts, and a scale arranged in
association with the X-ray indicating element, wherein said element and
scale are configured to allow placement on an exposure area for said
light and X-ray fields such as to allow determination of where on the
scale an edge of the light field and an edge of the X-ray field are
positioned when said fields are directed onto said exposure area. The
inventive arrangement comprises a digital camera arranged to generate an
image of the scale and the X-ray indicating element when the X-ray
indicating element emits light due to an exposure of said X-ray field.

[0016] The invention also concerns a device for determining alignment of a
light field and an X-ray field of an X-ray apparatus, said device
comprising an X-ray indicating element configured to emit light upon
exposure to X-rays in such a way that parts exposed to X-rays can be
distinguished from non-exposed parts, and a visible scale arranged in
association with the X-ray indicating element such as to allow
determination of where on the scale an edge of the light field and an
edge of the X-ray field are positioned. The inventive device comprises a
first and a second unit, wherein each of said units comprises a set of
said X-ray indicating element and scale, and wherein said first and
second units are rotatably connected to each other.

[0017] Such a device has the advantage that it can be positioned at two
edges of X-ray fields of different size and possibly four edges depending
on the particular design. A fewer number of X-ray exposures are thereby
needed to cover all edges compared to single units. Further, it takes a
minimum of space when folded together.

[0018] In a preferred embodiment of the inventive device it comprises four
units, each of which having an elongated shape and comprising a set of
said X-ray indicating element and scale, wherein said four units are
rotatably connected to each other such as to allow formation of a cross
and to allow positioning on top of each other. Such a device can be
adapted to most detection areas and dispenses with the need for a
detection screen that covers the entire detection area. Such screens are
relatively expensive and are not easy to carry around.

BRIEF DESCRIPTION OF DRAWINGS

[0019] In the description of the invention given below reference is made
to the following figure, in which:

[0020]FIG. 1 shows, in an exploded perspective view, a unit for
determining alignment of a light field and an X-ray field of an X-ray
apparatus,

[0021]FIG. 2 shows a composite device for determining alignment of a
light field and an X-ray field of an X-ray apparatus,

[0022]FIG. 3 shows a camera with supporting for use in the inventive
method and arrangement,

[0026]FIG. 1 shows, in an exploded perspective view, a unit 1 for
determining alignment of a light field and an X-ray field of an X-ray
apparatus. The unit 1 comprises an upper part 2, a mid part 4 and a lower
part 5 arranged together in a layered structure. A hole 8 goes through an
end part of the unit 1.

[0027] A scale 6 that extends in a longitudinal direction of the unit 1 is
visibly provided on the upper part 2. The scale 6 shows both units of
meters and inches with marks/scale divisions for millimeters as well as
for tenths of inches.

[0028] Roughly, the alignment determination unit 1 has a flat and
elongated shape, similar to a regular ruler.

[0029] The bottom part 5 is provided with an X-ray detectable scale 10
that has similar marks/scale divisions as the upper scale 6. The two
scales 6, 10 are horizontally adjusted in relation to each other such as
to be vertically aligned.

[0030] The bottom part 5 is made in a similar way as a printing wiring
board (PWB) where the scale 10 is made in cupper. Cupper absorbs and
scatters X-rays to a high extent which makes the lower scale 10 more or
less opaque to, and thereby detectable by, X-rays. Other materials and
elements, e.g. lead, are also well known to be detectable by X-rays.

[0031] The mid part 4 comprises a cutout 9 adapted to receive an X-ray
indicating element 3 that extends along, in this case below, the upper
visible scale 6 of the unit 1. The function of the mid part 4 is mainly
to work as a spacer and to hold the X-ray indicating element 3 in place.
Alternatively, it is possible to let the X-ray indicating element 3
constitute the entire mid part 4. A further function of the mid part 4 is
to provide a suitable background to at least a part of the scale 6.

[0032] The X-ray indicating element 3 is in this example a layered flat
unit that fluorescents upon exposure to X-rays, i.e. it emits light when
subjected to an X-ray field. Various light-emitting X-ray indicators are
commercially available. In this case the X-ray indicating element 3
comprises Gd2O2S:Tb which makes the indicator 3 sensitive and capable of
emitting reasonably large amounts of light even when subjected to a
relatively short and weak X-ray exposure. This is an advantage when using
a camera (see below) for producing an image of the emitting of light and
also makes it possible to use clinically relevant settings of an X-ray
apparatus during alignment determination. Further, the exemplified
indicating element 3 emits light during a rather short period of time,
less than 1 ms, after termination of X-ray exposure, which is an
advantage for dynamic X-ray distribution studies. A further advantage of
the X-ray indicating element 3 used here is that it is flexible.

[0033] Various types of fluorescent, phosphorescent or electronic (e.g.
X-ray sensor+light emitting diode) X-ray indicating elements are however
possible to use for the principle of the invention. Important is that
visible light is emitted upon exposure to X-rays and that the indicating
element has a reasonable extension length in at least one dimension such
that it can be placed across an edge of an X-ray field.

[0034] The X-ray indicating element 3 is configured to emit light upon
exposure to X-rays in such a way that parts exposed to X-rays can be
distinguished from non-exposed parts. This means that the element 3 when
placed across an edge of an X-ray field will exhibit a boundary line
during and shortly after X-ray exposure which boundary line corresponds
to the edge of the X-ray field and divides the element 3 into a
light-emitting exposed part and a non-exposed part that does not emit
light. The X-ray indicating element 3 described here has a high
resolution which means that the boundary line becomes as thin and sharp
as possible. How the X-ray indicating element 3 is used in the alignment
determination is further described below.

[0035] Main functions of the upper part 2 are to work as a carrier for the
upper scale 6 and to protect the underlying X-ray indicating element 3.
The upper part 2 is made of a plastic material and is transparent to
allow light emitted from the X-ray indicating element 3 to pass through.

[0036] The whole alignment determination unit 1 is flexible which e.g. is
advantageous if to be used on a rounded surface, such as a phantom.

[0037]FIG. 2 shows a composite device 11 for determining alignment of a
light field and an X-ray field of an X-ray apparatus according to the
invention. This composite device 11 is a combined set of, in this
particular example, four alignment determination units 1 hold together by
a hub member 13 placed in the hole 8 of each unit 1. The individual units
1 are rotatably connected to each other such as to allow formation of a
cross, as shown in FIG. 2, and to allow positioning on top of each other
such as to take up less space and be easier to carry around. The cross
formation shown in FIG. 2 is useful for placement across all four edges
of a rectangular light or X-ray field.

[0038] FIGS. 3-5 show a camera 20 arranged on a flexible arm 21 that is
connected to a fastening arrangement 23 for fastening the arm 21 and
camera 20 to an X-ray apparatus 30, as shown in FIGS. 4 and 5, or to
something else near to the X-ray apparatus 30. FIGS. 4-5 further show an
alignment determination unit 1 that has been positioned onto an exposure
area 16 that forms an upper surface of a digital X-ray screen detector
32. The alignment determination unit 1 forms in this example part of a
composite device 11 as shown in FIG. 2. The X-ray apparatus 30 shown in
FIGS. 4 and 5 is capable of generating both a light field 13 and an X-ray
field 12 for direction onto the exposure area 16 (see FIG. 5).

[0039] The flexible arm 21 makes it easy to adjust the camera 20 to
different X-ray apparatuses and to different settings of a certain
apparatus. In particular it is important to avoid that the camera 20
blocks the X-rays. The camera 20 is in this case adjusted such that its
field of view covers the entire exposure area 16.

[0040] The camera 20 is a high-resolution digital video camera that works
with the light of the visible spectrum. This means e.g. that it is
capable of recording a relatively high number of digital images per
second. The camera 20 is connectable (via cable or wire-less) to a
computer (not shown) for e.g. storing, viewing, processing and analyzing
of video clips and individual images recorded.

[0041]FIG. 5 shows both the light field 13 and the X-ray field 12
directed onto the exposure area 16. As indicated in FIG. 5, the X-ray
field 12 is slightly displaced in relation to the light field 13. Markers
15 have been positioned on each of the alignment determination units 1
such as to indicate the position of the light field 13 on the upper,
visible scale 6. The markers 15 are made of steel such as to be at least
partly opaque to X-rays and thereby be detectable by X-rays.

[0042] The displacement and distorsion, i.e. the lack of alignment, of the
light and X-ray fields 13, 12 indicated in FIG. 5 is more clearly shown
in FIG. 6 which shows a magnified view of a part 25 of FIG. 5 (indicated
with a dashed line in FIG. 5). As can be seen in FIG. 6, an edge 120 of
the X-ray field 12 is displaced somewhat to the left of an edge 130 of
the light field 13. The marker 15 indicates the position on the scale 6
where the light field edge 130 is positioned.

[0043] In the following a preferred method for determining the alignment
of the light field 13 and the X-ray field 12 of the X-ray apparatus 30
will be described. Initially, the steps of directing the light field 13
onto the exposure area 16 and positioning/adjusting the composite
alignment determination device 11 such that each individual alignment
determination unit 1 crosses an edge 130 of the light field 13 are
performed.

[0044] In a following step, the position on the scale 6 where the light
field edge 130 is positioned is registered on each unit 1 by placing the
marker 15 such as to indicate said position on the scale 6. At this stage
the light field 13 can be turned off or blocked.

[0045] In a following step recording with the digital video camera 20 is
started. As described above, the camera 20 is adjusted such that its
field of view covers the entire exposure area 16 which means that all
X-ray and light field edges 120, 130 and all scales 6 and markers 15 are
captured on the video recording.

[0046] In a following step an X-ray exposure is made by directing the
X-ray field 12 onto the exposure area 16 during a certain time period
typically around 100 ms. In a following step the video recording is
stopped, i.e. the camera 20 is stopped or paused. The video recording is
stored on a computer readable medium and transferred to a computer (not
shown).

[0047] In a following step the video recording is viewed and analyzed
using image/video processing software installed on the computer. The
software allows image by image viewing on a screen connected to the
computer. Various software suitable for this purpose are commercially
available.

[0048] Storing and transferring of the video recording can be carried out
in many different ways. For instance, the recording can initially be
stored in a memory of the camera 20 and thereafter be transferred via
cable or wire-less to a computer. A skilled person in the art is familiar
with storing and transferring of video recordings.

[0049] By viewing and analyzing the recorded video clip it is possible to
select one or several images (out of the plurality of images forming the
video clip) of the set of alignment determination units 1 showing the
X-ray indicating element 3 emitting light due to the X-ray exposure.
Since parts of the X-ray indicating element 3 positioned outside of the
X-ray field 12 will not emit any light, such an image will show the
position on the scale 6 where the edge 120 of the X-ray field 12 is
positioned, i.e. where the boundary line is positioned, with the current
settings of the X-ray apparatus 30.

[0050] Generation of such an image can be made also with a single-shot
digital camera but this is likely to require either automatic trigging of
the camera, which is complicated, or an X-ray indicating element 3 that
emits light during a much longer time period, which e.g. reduces the
possibility of performing dynamic X-ray distribution studies.

[0051] By using an adequate image processing software it is possible to
zoom into interesting portions of the image such as to determine the
position of the X-ray field edge 120 in more detail. The camera 20 should
have a sufficient resolution and be positioned sufficiently close to the
exposure area 16 such that the position of the X-ray field edge 120 can
be determined within 1 mm, i.e. the mm scale divisions of the scale 6
should be visible on the computer screen when analyzing the image.

[0052] At this stage it is possible to compare the scale positions of the
edges 130, 120 of the light and X-ray fields 13, 12. Thereby the degree
of alignment of the light field 13 and the X-ray field 12 can be
determined. If the alignment is not sufficient, typically within 2 mm,
the X-ray apparatus 30 is adjusted (which is a known procedure and
therefore not described here).

[0053] In the preferred method a user determines the position of the edge
120 of the X-ray field 12 simply by visually viewing an image on a
screen, if necessary with the aid of zooming. This task may be possible
to carry out with a computer program that analyses the image and
automatically identifies and calculates the position of the edge 120 in
relation to the scale 6. However, such an automated method would require
complicated calculation algorithms that take account of the position of
the camera. Even a minor adjustment of the position of the camera that
changes its distance and/or angle to the exposure area 16 would require
extensive calculations to compensate for the different camera position.
The preferred method eliminates these problems and allows for a
relatively free positioning of the camera 20.

[0054] In order to generate a useful image of the scale 6 and the edge 120
of the X-ray field 12 it is necessary that the scale 6 is visible, i.e.
that some light is present. This can e.g. be achieved by having some
background light in the room where the X-ray apparatus 30 is located, by
leaving the light field 13 on during X-ray exposure, or by configuring
the alignment determination unit 1 such that the X-ray indicating element
3 illuminates the scale 6 when subjected to the X-ray exposure. Further,
also the scale 6 itself may be configured to emit light upon exposure to
X-rays. Of course, the light used to visualize the scale 6 should be
limited such that the light emitted from the X-ray indicating element 3
still can be detected.

[0055] The present invention provides for a simple and thorough
documentation since all digital images and video clips easily can be
stored on a computer readable medium. As an alternative or complement to
storing all images and video clips, values of the scale positions of the
field edges 120, 130 can be stored.

[0056] The unit 1 and device 11 for determining the alignment of the light
field 13 and the X-ray field 12 of the X-ray apparatus 30 can also be
used in an alternative method where the digital X-ray screen detector 32
is used instead of the camera. The initial steps of this method are
similar to what is described above, i.e. i) directing the light field 13
onto the exposure area 16, ii) positioning/adjusting the composite
alignment determination device 11 such that each individual unit 1
crosses an edge 130 of the light field 13., and iii) registering the
position on the scale 6 where the light field edge 130 is positioned is
registered by placing the marker 15 such as to indicate said position on
the scale 6. Also the step of turning off the light field 13 can be
similar. An additional step may be to activate the digital X-ray screen
detector 32.

[0057] The next step in this alternative method is to perform an X-ray
exposure directing the X-ray field 12 onto the exposure area 16 during a
certain time period, typically around 100 ms. This step is followed by a
step including an analysis of the detector image produced by the digital
X-ray screen detector 32. On this detector image the X-ray field 13, the
X-ray detectable scale 10 of each unit 1, as well as each marker 15 will
appear. By analyzing this detector image and comparing the positions of
the field edges 120, 130 in relation to the X-ray detectable scale 10 it
is possible to determine the alignment of the light field 13 and the
X-ray field 12 of the X-ray apparatus 30.

[0058] In a variant of this alternative method it is carried out without
using the light field 13. In such a case the alignment determination
device 11 and the markers 15 are initially positioned according to
certain marks on top of the detector 32.

[0059] The camera 20 can be used in combination with the variants of the
alternative method in that the camera 20 can be used for registering the
light field 13 and/or the image of the detector 32 (e.g. by recording an
image of a monitor connected to the detector 32).

[0060] The invention is not limited by the embodiments described above but
can be modified in various ways within the scope of the claims. For
instance, it is not necessary for the inventive method that a composite
alignment determination device 11 is used; one or several individual
alignment determination units 1 may be used. Neither is it necessary that
the scale 6 and the X-ray indicating element 3 are integrated into the
same unit 1 such as shown in FIG. 1, although such a unit simplifies the
procedure. What is important is that the scale 6 and element 3 are
arranged in association with each other, preferably along each other,
such that the position on the scale where an edge of the X-ray field is
positioned can be determined.

[0061] Moreover, the position on the scale 6 where the light field edge
130 is positioned does not necessarily have to be registered by placing a
marker but can e.g. be registered by generating an image using the camera
20. This image can then be compared to the image showing the position of
the X-ray field edge 120. In principle, this registration can of course
also be made by making a note, mental or physical.

[0062] Viewing and analyzing videos and images do not necessarily have to
be performed in connection to the light and X-ray field exposures. The
camera recordings can e.g. be stored on a portable computer or memory,
and be viewed and analyzed at a later stage in a different location. Of
course, recorded data can also be sent and stored using a data network,
such as a local computer network. Thus, it is not necessary that the
computer used to analyze the data is connected to the camera 20.

[0063] Individual alignment determination units 1 can be put together to
composite devices 11 that have more or fewer than four individual units
to suit different applications. For instance, a fifth shorter alignment
determination unit 1 may be added that is suitable for mammography.